This invention relates generally to techniques for providing electrical components on printed circuit boards or cards.
In a wide variety of electronic devices, space is often at a premium in order achieve small device size. This is particularly true in a variety of computer applications and most particularly true in connection with portable computers.
The demands for available board space has increased with the introduction of the Pentium.RTM. II brand processor from Intel Corporation. This processor uses Gunning transceiver logic ("GTL"), which requires parallel resistive terminations for all GTL signals. The number of GTL signals between the processor and bridge can be in the range of 150, each of which must be connected to a parallel pull up resistive termination. Decoupling capacitors are typically utilized to provide high frequency capacitive decoupling in computer systems. From 30 to 40 decoupling capacitors may be needed in a portable computer using GTL. Thus, the demands for limited PCB or card space are strained even further by the additional device requirements brought on in recent vintage processors.
Ball grid array ("BGA") packages have become increasingly popular for a large variety of applications Fundamental limitations on wire bonding technology and pad pitch have made some existing industry standard packages, such as plastic quad flat pack ("PQFP") packages, technology roadblocks when the input/output pin count must exceed 250 to 300. In addition, BGA packages can have internal ground and power planes for high frequency operation. These internal planes provide impedance control, limiting the effective inductance seen by the silicon device. This may increase the useable operating frequencies of the silicon device due to the reduction of package related noise and cross-talk.
While there are a wide variety of options available in the general field of BGA's, there are two well known BGA packages. One BGA package uses an over molded pad array carrier ("OMPAC") while the other uses a substrate material that is ceramic ("CBGA"). Generally, BGA packages include a die carrier and a plurality of solder balls or bumps beneath the die carrier which connect to contacts formed on a board or card. These contacts may communicate via metal lines with vias which extend through the board. The portion of the board on the underside of a BGA package is generally too populated with via holes to provide useful space for additional devices.